Allow pathname filtering for DEBUG (only) level logging messages.

Currently enabling DEBUG level logging produces so much content that we can quickly exhaust logs.  The volume makes analysis of DEBUG level logs daunting at the very least.  We also tend not to leave useful debug messages in the code knowing full-well that too much volume may be produced.

The aim here is to add filtering on the caller's pathname in the DEBUG level wrapper functions.  Whilst undoubtedly there will be some performance impact, this shouldn't matter give it is only for DEBUG level logging.  It should also mean we can hone in on a area permitting greater use of debug logging for diagnostic purposes.